Earlier this year, Apple said it would dump Google's mapping software from its mobile devices.
Google is also the maker of the most popular smartphone software with its Android operating system. In May, Google closed the $12.5 billion acquisition of Motorola Mobility, setting the stage for Google to more tightly integrate its smartphone software and hardware and mount a more direct challenge to Apple's iPhone.
Apple said in a statement on Monday that its license to include the YouTube app in the iOS operating system "has ended." Apple noted that "customers can use YouTube in the Safari browser and Google is working on a new YouTube app to be on the app store."
YouTube is one of the most popular destinations on the Internet, with more than 800 million unique monthly visitors who stream 4 billion videos a day.
Google said in a statement that it was working with Apple to ensure that it has "the best possible YouTube experience for iOS users."